In recent years, high intensity lamps, such as xenon lamps and sodium lamps, used as the light sources of lighting devices such as vehicle headlamps and exterior lighting devices are being replaced with semiconductor light emitting apparatuses (for example, such as LEDs) that have long life and low power consumption. Therefore, there is a demand for higher power LED lighting devices including LEDs as light sources.
Most xenon lamps currently in widespread use have an output power of about 200 W to about 2000 W. Therefore, the power inputted to LED lighting devices that are replacing the xenon lamps is also increasing. Recent development shows that the power inputted to one LED lighting device can be greater than 200 W.
As the power of LED lighting devices increases, the amount of heat generated from the LED light sources increases. Since the light conversion efficiency of the LED light sources is lowered and life thereof is shortened with temperature increases, an important task is to develop a cooling structure for reducing the temperature of the LED light sources to drive them stably. For example, in a cooling structure proposed in Japanese Patent Application Laid-Open No. 2002-299700, an LED-mounted substrate is pressed against and secured to a metal heat dissipating-securing plate by a metal heat dissipating cover, and the heat dissipating-securing plate, which has the LED-mounted substrate secured thereto, is disposed in a sealed space formed by a light-transmitting cover and a resin case. A plurality of heat dissipating fins are formed on the heat dissipating-securing plate. In this structure, the heat generated from the LED light sources is transferred to the heat dissipating-securing plate through the LED-mounted substrate and through the heat dissipating cover. The heat transferred to the heat dissipating-securing plate is dissipated into the atmosphere through the heat dissipating fins and the resin case, and the LED light sources are thereby cooled.
However, with the above natural cooling-heat dissipating structure, a high cooling effect is not expected, and, thus, there is a limit to the increase in the output power.
In view of the above, a liquid cooling system that cools LED light sources by circulating cooling liquid through a closed circulation path is proposed (for example, see Japanese Patent Application Laid-Open No. 2006-047914). This liquid cooling system includes a heat receiving jacket, a radiator, a circulation pump, a reserve tank, and a fan. The cooling liquid is circulated through the circulation path by the circulation pump and receives the heat generated from the LED light sources when passing through the heat receiving jacket. The cooling liquid, increased in temperature due to reception of heat generated from the LED light sources, is then cooled in the radiator by heat exchange with outside air. In this system, the above cycle is repeated to liquid-cool the LED light sources.
Referring to FIGS. 1 to 3, a description will be given of the basic configuration of a liquid-cooled LED lighting device having the above liquid cooling system and its control flow when the device is turned on and off.
FIG. 1 is a block diagram illustrating the basic configuration of the power supply system of the conventional liquid-cooled LED lighting device. An LED on-off switch 127 is connected to a power supply (main power supply) 126 such as a commercial power supply. An LED light source-driving power supply 128 for supplying power to LED light sources 110 and a liquid cooling system-driving power supply 130 for supplying power to a fan and a circulation pump 103 of the cooling system are connected in parallel to the LED on-off switch 127.
FIG. 2 is a flowchart showing the control flow when the liquid-cooled LED lighting device is turned on. As shown in FIG. 2, the main power supply 126 is turned on (step S41) and the LED on-off switch 127 is switched on (step S42). Thereby, the LED light source-driving power supply 128 and the liquid cooling system-driving power supply 130 are simultaneously turned on (steps S43 and S44). Therefore, the LED light sources 110 are turned on (step S45), and the liquid cooling system 103 (including a fan, a pump, and the like) is actuated to cool the LED light sources 110.
FIG. 3 is a flowchart showing the control flow when the liquid-cooled LED lighting device is turned off. As shown in FIG. 3, when the LED on-off switch 127 is switched off (step S51), the LED light source-driving power supply 128 is turned off, and the LED light sources are turned off (step S52). At the same time, the liquid cooling system-driving power supply 130 is turned off, and the fan and the circulation pump of the liquid cooling system 103 are stopped (step S53). Then the entire operation of the liquid cooling LED lighting system is stopped (step S54).
In the conventional liquid-cooled LED lighting device, at the same time as the LED on-off switch 127 is switched off, the liquid cooling system-driving power supply 130 is turned off, and the fan and the circulation pump of the liquid cooling system 103 are stopped, as shown in the flowchart in FIG. 3. Therefore, the efficiency of dissipation of the heat received by the cooling liquid to the outside air is significantly reduced. In addition, since the circulation of the cooling liquid is stopped, the flow of heat to the components connected to the heat receiving jacket and those in the downstream side are interrupted, and this results in thermal insulation.
A general liquid-cooled LED lighting device is required to have heat dissipation performance that ensures that the temperature of the LED light sources is maintained at 150° C. or less. Under normal operation, the temperatures of the heat receiving jacket and the cooling liquid contained therein are midway between the temperature of the LED light sources and the temperature of ambient air. Therefore, assuming that the temperature of outside air is about 20° C., the temperature of the liquid cooling system is about 85° C. at maximum.
Therefore, when, as described above, the heat receiving jacket is thermally insulated because the liquid cooling system is stopped at the same time as the LED light sources are turned off, the heat accumulated in the LED light sources and the heat receiving jacket is not dissipated from the radiator. Although the temperature of the LED light sources does not increase, the temperature of the heat receiving jacket and the cooling liquid therein temporarily increases. This heat is transferred through the liquid in tubing, resulting in an increase in the temperature of other components such as the circulation pump and rubber hoses.
Table 1 shows the results of the measurement of the temperatures of the components (LED light sources, heat receiving jacket, circulation pump, and radiator) of the conventional liquid-cooled LED lighting device when the device is ON and just after the device is turned off (outside air temperature: 25° C.).
TABLE 1Just after deviceWhen device is ONis turned offLED light sources150° C. 130° C. Heat receiving jacket85° C.110° C. Circulation pump60° C.80° C.Radiator45° C.45° C.Outside air25° C.25° C.
For example, the temperature of the rubber hoses temporarily increases to about 110° C., which is higher than their heat resistant temperature. This causes a reduction in the reliability of the device. As the temperature of the cooling liquid increases, its volume increases. Therefore, the volume of the cooling liquid passing through the rubber hoses increases. This causes a problem in that the size of the reserve tank should be increased.
The life of the circulation pump is known to be largely affected by temperature. As described above, when the LED light sources are turned off and at the same time the liquid cooling system is stopped, the temperature of the circulation pump temporarily increases to about 100° C. This also causes a reduction in the reliability of the device.
Furthermore, in the LED lighting device with the above configuration, the temperature of the cooling liquid depends on the temperature of ambient air, assuming that the heat dissipation performance of the lighting device is not varied. In this case, as the temperature of the ambient air increases, the temperature of the cooling liquid is also increased, resulting in the increase of the LED temperature when the LEDs are turned on. As a result, the light conversion efficiency may deteriorate, and accordingly, the illumination intensity may also deteriorate. At the same time, the life of the LED device is also shortened.
In addition to the temperature change of ambient air, several causes that can lower the heat dissipation performance over time may be involved. Examples of the causes include variations in the flow rate of the pump, the rate at which the fans blows air, and the LLC concentration of the cooling liquid, etc. Accordingly, the liquid-cooling system is likely to be affected by temperature changes during operation of the LED as compared with heat dissipation caused by a heat dissipation structure utilizing an air cooling mechanism (such as a heat sink) with natural heat dissipation. This system poses a problem in that a stable illumination intensity and life cannot be ensured.
Furthermore, if the circular pump and/or the fan do not properly operate due to unexpected external causes, breaking of the power supplying wire, and/or the expiration of its useful life, heat generated by the LEDs cannot be transferred from the heat receiving jacket to the downstream components. This means that the entire temperature of the components of the heat dissipation structure, including LEDs increases. In some worst cases, the temperature of cooling liquid may exceed its boiling point, which may cause the tubing to be broken, leading to liquid leakage.
Lighting devices for use in dangerous areas such as chemical plants, mine cavities, areas where dangerous objects should be handled, gas stations, oil storages, manholes, tunnels, factories for fireworks production, ammunition dumps, and the like generally use, as their light source, metal halide lamps, high-pressure mercury lamps, halogen lamps, and other discharge type light source lamps. Such lighting devices have been provided with various countermeasures for preventing surrounding flammable gases from catching fire. For example, in Japanese Patent Publication No. 4099603 (B), an explosion protection lighting device has been proposed, in which socket holders are disposed at respective ends of a main body, and a straight-tube lamp is disposed between the socket holders while the lamp is enclosed within a lamp protection cylinder.
However, it is difficult for a conventional lighting device that utilizes a discharge type light source lamp to completely prevent the occurrence of explosions caused by a lamp burst. Accordingly, in order to lower the risk of explosion as much as possible, several explosion-protection structures have been developed, but these have not provided sufficient protection.
Furthermore, such a structure may require a thick glass member that has an increased strength for the discharge type light source lamp, and may employ complex connecting structures for components to enhance the hermeticity. These structures may have a disadvantageously increased weight or volume caused by the used lamp.
Furthermore, since the discharge type light source lamp should be periodically replaced with a new one, there is a problem because maintenance, such as replacement of the lamp, may take a large amount of time and labor due to the complex structures, as described above.
The presently disclosed subject matter was devised in view of these and other problems and in association with the conventional art. According to an aspect of the presently disclosed subject matter, a liquid-cooled LED lighting device can be provided in which a temporal increase in the temperature of the tubing and the circulation pump when the LED light sources are turned off is prevented to ensure high reliability.
According to another aspect of the presently disclosed subject matter, the liquid-cooled LED lighting device can suppress excess temperature increases when the LED light sources are turned off to maintain a stable state, thereby achieving stable output illumination intensity and life. Furthermore, the liquid-cooled LED lighting device can ensure the safety of the device, including the LED light sources by interrupting the drive current if the temperature of the cooling liquid abnormally increases.
According to still another aspect of the presently disclosed subject matter, the liquid-cooled LED lighting device can be used in a dangerous area while the device can prevent possible explosion risks and also facilitate the maintenance thereof.
According to still another aspect of the presently disclosed subject matter, a liquid-cooled LED lighting device can include: an LED light source, a liquid cooling system including a heat receiving jacket and a radiator, an LED light source-driving power supply configured to supply power to the LED light source, a liquid cooling system-driving power supply configured to supply power to the liquid cooling system, and a control unit configured to control at least one of the LED light source-driving power supply and the liquid cooling system-driving power supply.
In the liquid-cooled LED lighting device as configured above, the control unit can control and maintain the supply of power from the liquid cooling system-driving power supply to the liquid cooling system for a predetermined period of time after supply of the power from the LED light source-driving power supply to the LED light source is stopped.
The liquid-cooled LED lighting device as configured above can further include an LED on-off switch configured to transmit an ON signal and an OFF signal to the control unit, and the control unit can include a timer circuit configured to be activated in response to the OFF signal transmitted from the LED on-off switch. In this configuration, the control unit can maintain the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system for the predetermined time in response to an output signal from the timer circuit.
In the liquid-cooled LED lighting device as configured above, the control unit can include a temperature control circuit including a temperature detection element that is secured to one of the LED light source, the heat receiving jacket, and a metal base in contact with the heat receiving jacket. In this configuration, the control unit can maintain the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system for a period of time in response to an output signal from the temperature control circuit.
In the liquid-cooled LED lighting device as configured above, when a temperature detected by the temperature detection element after the supply of the power from the LED light source-driving power supply to the LED light source is stopped is higher than a first predetermined threshold value, the control unit can maintain the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system until the temperature detected by the temperature detection element is equal to or lower than the first predetermined threshold value.
In the liquid-cooled LED lighting device as configured above, if a temperature detected by the temperature detection element at a time when the supply of the power from the LED light source-driving power supply to the LED light source is started is lower than a second predetermined threshold value, the control unit can prevent the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system until the temperature detected by the temperature detection element is equal to or higher than the second predetermined threshold value.
Alternatively, in the liquid-cooled LED lighting device configured to include the basic components as above, the control unit can include a temperature control circuit including a temperature detection element that is secured to one of the LED light source, the heat receiving jacket, and a metal base in contact with the heat receiving jacket. In this configuration, the control unit can control a drive current for the LED light source based on a temperature detected by the temperature detection element. Furthermore, the control unit can control the drive current for the LED light source to be within a range of from zero (0) to a normal LED drive current.
Still alternatively, the liquid-cooled LED lighting device configured to include the basic components as above can be used to illuminate an area where a flammable gas having a flash point is present. In this liquid-cooled LED lighting device, the temperature detection element can be secured to the LED light source to detect a temperature of the LED light source, and the control unit can control at least one of the LED light source-driving power supply and the liquid cooling system-driving power supply to maintain the temperature of the LED light source to be lower than the flash point of the flammable gas. In this case, the control unit can control the temperature of the LED light source so that the highest temperature of the LED light source at its emission portion is equal to or lower than 95° C.
In the liquid-cooled LED lighting device as configured above, the temperature detection element can be any of a thermistor and a temperature detection IC.
The liquid-cooled LED lighting device as configured above can further include a pilot lamp configured to be turned on when the liquid cooling system is stopped by interruption of the supply of the power from liquid cooling system-driving power supply to the liquid cooling system.
The liquid-cooled LED lighting device as configured above can further include an air cooling heat dissipation system. In this case, the heat receiving jacket can be disposed between the LED light source and the air cooling heat dissipation system.
The liquid-cooled LED lighting device as configured above can further include a metal circuit casing configured to cover the control unit for controlling the drive of the LED light source, the LED light source-driving power supply, and the like. In this case, the circuit casing can include an atmospheric heat dissipation portion. Furthermore, the circuit casing can be disposed so as to be in close contact with the heat receiving jacket. Then, the atmospheric heat dissipation portion formed in the circuit casing can serve as the air cooling heat dissipation system.
Alternatively, the heat receiving jacket can be provided with an atmospheric heat dissipation portion. In this case, the atmospheric heat dissipation portion formed in the heat receiving jacket can serve as the air cooling heat dissipation system.
In the liquid-cooled LED lighting device as configured above, the atmospheric heat dissipation portion can be composed of a heat dissipation pin and/or a heat dissipation fin.
In the liquid-cooled LED lighting device including the air cooling heat dissipation system as configured above, if the liquid cooling system does not work properly, the control unit can control the LED light source-driving power supply so that the detected temperature of the LED light source can be maintained lower than the flash point of the flammable gas through only the air cooling heat dissipation system. In this case, the control unit can control the current to be supplied to the LED light source to a value such that heat generated by the LED can be absorbed by the air cooling heat dissipation system.
Furthermore, in the liquid-cooled LED lighting device as configured above, the liquid cooling system can further include a circulation pump, a reserve tank, and a fan.
According to one aspect of the presently disclosed subject matter, the liquid-cooled LED lighting device as configured above can include a control unit configured to control at least one of the LED light source-driving power supply and the liquid cooling system-driving power supply. This configuration can provide an appropriate cooling effect by controlling the system in various ways. For example, even after the supply of the power from the LED light source-driving power supply to the LED light source is stopped and the LED light source is turned off, the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system is controlled to be maintained for a predetermined period of time so that the fan and the circulation pump can remain energized. Therefore, a temporal increase in the temperature of the tubing such as rubber hoses and the circulation pump can be prevented, and the reliability of the liquid-cooled LED lighting device can be improved.
Furthermore, in the liquid-cooled LED lighting device as configured above, even after the LED light source is turned off, the fan and the circulation pump of the liquid cooling system can remain activated for a period of time set by the timer circuit. Therefore, a temporal increase in the temperature of the tubing such as the rubber hoses and the circulation pump is prevented, and this ensures high reliability of the liquid-cooled LED lighting device.
In the liquid-cooled LED lighting device as configured above, when the temperature detected by the temperature detection element after the LED light source is turned off is or higher than a predetermined threshold value, the supply of the power to the liquid cooling system is maintained until the temperature detected by the temperature detection element is equal to or lower than the predetermined threshold value. Since the fan and the circulation pump remain energized during this period, the tubing such as the rubber hoses and the circulation pump can be cooled to a preset temperature in a reliable manner.
In the liquid-cooled LED lighting device as configured above, under cool conditions in which the temperature detected by the temperature detection element when the LED light source is turned on is lower than a predetermined threshold value, the power is not supplied to the liquid cooling system until the temperature detected by the temperature detection element is equal to or higher than the predetermined threshold value. Since cooling is not effected during this period, the entire liquid-cooled LED lighting device can be rapidly warmed to the required operating temperature.
In the liquid-cooled LED lighting device as configured above, the control unit can be provided with a temperature detection element, and can control the drive current for the LED light source based on a temperature detected by the temperature detection element. In this case, the LED drive current can be controlled within a range of from zero to a normal LED drive current. This control can suppress the excessive temperature increase when the LED light source is driven. As a result, the lighting device can utilize a higher power LED light source and ensure the stable illumination intensity and life as well as the high reliability of the device.
When the liquid-cooled LED lighting device is used in the area where a flammable gas with a certain flash point is present, the liquid-cooled LED lighting device can have a liquid cooling system disposed adjacent to the light source portion, including LEDs, and can control at least one of the LED light source-driving power supply and the liquid cooling system-driving power supply to maintain the temperature of the LED light source (the highest temperature of the LED light source at its emission portion) to be lower than the flash point of the flammable gas (for example, equal to or lower than 95° C.). Accordingly, even when the liquid-cooled LED lighting device of the presently disclosed subject matter is used in a dangerous area, it is possible to prevent possible explosion risks due to catching fire of the surrounding flammable gas.
The liquid-cooled LED lighting device of the presently disclosed subject matter utilizes as its light source an LED(s) that is substantially maintenance free. Accordingly, the replacement of light sources can be eliminated, thereby facilitating the maintenance thereof.
In the liquid-cooled LED lighting device as configured above, the temperature of any of the LED light source, the heat receiving jacket, and the metal base in contact with the heat receiving jacket is correctly detected by the thermistor or the temperature detection IC, and the liquid cooling system can thereby be appropriately controlled.
In the liquid-cooled LED lighting device as configured above, the liquid cooling system can remain energized for a predetermined time after the LED light source is turned off. Subsequently, when the supply of the power to the liquid cooling system is stopped and the liquid cooling system is stopped, the pilot lamp is turned on to indicate this condition. Therefore, a main power source switch can be switched off after the state of the pilot lamp is checked.
In the liquid-cooled LED lighting device as configured above, when the liquid cooling system, having operating portions such as a circulation pump and a fan, cannot work properly due to some accidents (namely, the cooling function is damaged), the control unit can control the current to be supplied to the LED light source to a value such that heat generated by the LED can be absorbed by the air cooling heat dissipation system. Accordingly, overheating of the LED can be prevented. In this case, although the illumination intensity may be lowered due to the suppressed current, the maximum temperature of the light source can be controlled to be lower than the flash point of the surrounding flammable gas. Thus, even when the liquid-cooled LED lighting device of the presently disclosed subject matter is used in a dangerous area, it is possible to prevent possible explosion risks.